There are many website, such as Newbetakey.com, which claim to offer codes for Simpoints, however it is unlikely that the codes which can be found on sites like these will work.
Instead, I've outlined some of the options for getting Simpoints below:
Why is it unlikely that you'll find a code for Simpoints?
Simpoints are in game currency which users pay for to enhance their gaming experience. The creators of Sims 3 will have gone to great lengths to ensure that their system can't be cheated, so they make the most money, and minimize their losses from theft!
As previously mentioned, Simpoints are purchased, and so it's unlikely the free codes on websites which claim to offer them will be valid, as this would only cost them money.
What are the options?
You can trawl endless sites claiming to offer codes for Simpoints, but I wouldn't get your hopes up, as many of these will simply not be valid. You may also be able to download a code from a torrent site, but again it will be unlikely that you will come across a valid code. You also run the risk of downloading something more unwelcome like a virus.
The only sure fire way to get your hands on Simpoints is to pay for them, and whilst it may cost you in money, it will save you in time and effort.